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Unsuccessful charge attempt- compressor siezed

MikeC5 on Sat November 07, 2009 7:32 PM User is offlineView users profile

Year: 85
Make: Porsche
Model: 944
Engine Size: 2.5 L
Refrigerant Type: R12
Ambient Temp: 65 F
Pressure Low: 55
Pressure High: 55

I guess I'm learning the hard way. I tried charging the system today after rebuilding the compressor, installing new AC hoses, new drier, and flushing the evap and condenser (while removed from car). I used ester oil with R-12. Total system capacity is listed as 9.3 oz oil and I put 4 in the compressor (Nippondenso 6E171), 2 in the high side line and the rest in the drier.

Prior to installing the new drier the system was evacuated to 29.9+ for a half hour which it held for an hour. I then put in the new drier and pulled it down again to 29.9+ for a half hour. I charged (into the vacuum) one 12 oz can of R12 on the high side (not running) and my gauges equalized at about 55 psi.

I then started the car, turned on the AC to max and the clutch did engage. I started charging a 2nd can into the low side and noticed the pressures were not changing much. The low side increased a few psi and the hi side none at all. I tried bringing up the revs a bit but it still didn't seem to be taking more charge. Maybe 2 minutes elapsed before I shut the low side valve and tried to figure out what was wrong. Maybe a minute later the engine stalls. I turn off the AC, re-start the car and when I turned on the AC again it stalls the engine.... a bowl full of not good...

After things cooled down (compressor was HOT), I put a socket on the compressor and found it will only rotate back and forth about 3/4 of a revolution. After that in either direction it ain't moving!

So time for a 'post mortem' analysis of what I did wrong... It could have been a bad compressor to start with. It came form a junkyard with no known history, however, it looked clean inside and the residual oil in there was clear. I didn't see any obvious signs of wear, cylinders looked good, swash plate good, etc. New O-rings, front seal and clutch bearing. 4 oz of ester oil added to low side and I tested it by capping the hi side and putting a gauge on the low side and turning it around 10 rpm with electric drill. It produced around 20 in Hg vacuum.

I did flush the evaporator with the expansion valve in place. A bad move? I sprayed the flush solvent into the inlet, shook it around a bit, let it sit for several minutes and then applied compressed air (approx 90 psi) to force it through to evap outlet. Since it did come out I assumed this proved the exp valve was not plugged.

I'm hoping to learn what likely caused the compressor to seize so quickly. Was my method of charging flawed somewhere? Should I have just put all of the oil in the compressor? This was the first time I ever tried to charge up a system from complete disassembly, flush, etc.

bohica2xo on Sat November 07, 2009 8:52 PM User is offline


The first thing you are going to hear about here (over & over) is the flushing operation, and the probability of flush agent returning to the compressor. I will leave the discussion of that for later, I am sure Iceman & Karl are on the way...

Why did you stop at one can of liquid? You had a chance to get most of a second can in if you only had 55 psi static. Get as much of the charge in as you can before starting the pump.


"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

MikeC5 on Sat November 07, 2009 9:58 PM User is offlineView users profile

It took some time and warming of the can to get all of the first one in. I just didn't think I could get much more in that way. I'm pretty sure all of the flush agent was gone. I pushed compressed air through the evap until there was no trace coming from the outlet. I also pushed air through in the reverse direction to be sure none was still in there (maybe this was bad for the exp valve?). And it was a week before the evap was installed after flushing. Even if a small amount was in there wouldn't it boil off during evac? The stuff seemed to evaporate fairly quickly when spilled on the floor.

bohica2xo on Sat November 07, 2009 11:31 PM User is offline

Ah. Warming should not be necessary if you charge liquid into the high side. It should go into the vacuum quickly - the can barely gets cold. Once the system equalized @ 58 psi, a warm can of liquid @ 125 psi should feed right in too.


"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

HECAT on Sun November 08, 2009 8:29 AM User is offline

OUCH, learning is great.

You can build that compressor again, but I quit trying years ago. I tend to take my lumps learned and move on from lessons in frustration.

I put almost the full charge into vacuum on the last job I did (small system).

Signs (clutch engaged with low charge, low side rise, no high side) were indicating something was off in this charging procedure or the system was not working properly. Time to shut it down and step back to analyze. Letting it run for 3 or more minutes including revs probably ran the compressor dry. It pumped out the oil that was in it and without more of a charge in there, no more oil was migrating back into it. Smoked it! I would buy a new one. Your "post mortem" will determine if your condenser is now full of metal.

Bad move? Yes. Flushing through a TXV kills the process. There is now way to push the flush in with any velocity through the orifice; it just becomes a trickle fill. The orrifice also restricts the evaporative velocity of the air blow. Doing this in car will often leave a volume of solvent ready to flush your compressor on start up. You shook it around? Indicates you flushed this Evap out of the car, and that the TXV would be easy to and should have, been removed.

Assuming you shook the Evap around some with your air blow, this may have aided more to come out. It also seems you used a highly evaporative spray can flush, and it aired for a week. A/C purposed spray can flushes use HFC's. If you were removing old mineral oil, this would not be the right flush. Only a rare few flush chemicals with lower boiling points will be removed under vacuum.

Just my thoughts, good luck with your failure anlysis.


HECAT: You support the Forum when you consider for your a/c parts.


MikeC5 on Sun November 08, 2009 8:54 AM User is offlineView users profile

Yea I don't think I'll be rebuilding that one... I'm definitely going to get a new TXV and am crossing my fingers that the compressor didn't have enough time to spew debris into the system. I thought about changing the TXV but didn't think it necessary. Is there a way to test them once you remove?

mk378 on Sun November 08, 2009 5:26 PM User is offline

What HECAT was saying is that you MUST disconnect the TXV in order to flush an evaporator. If you try to blow through the TXV, you won't get enough flow to get the flushing agent out of the evaporator core.

MikeC5 on Sun November 08, 2009 5:49 PM User is offlineView users profile

Yes I understand the mistake now. I should have removed the TXV for a proper flush and by not doing so I may very well have left solvent in there and who knows what else...

MikeC5 on Wed November 11, 2009 10:09 PM User is offlineView users profile

Well, well... the compressor post mortem was simple and the news wasn't bad (relatively speaking). It tuns out one of the reed valve mount nuts loosened and liberated itself (DOD - domestic object damage). It eventually found its way into one of the cylinders and the piston proceeded to squash it but good (at first I thought it was a woodruff key). The good news is that nothing seized in there, there was still around 3.5 oz of clean oil and it didn't run long enough to even scrape up the cylinder wall. Why did the nut come loose? When I originally disassembled the thing the reed valve plate didn't want to come out. Not knowing any better, I thought the exposed nuts were threaded onto studs holding the plate down. I removed one and then quickly realized they were part of the reed valve retainment. Once I finally did get the reed valve plate out I put the nut back on and tightened it good (so I thought). Hey it would have been nice to say I successfully rebuilt an AC compressor first time out of the box but at least I learned something... I still plan to replace the TVX though.

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